Fixed kleene star behavior, which used to behave like a '+'

main.go

@@ -9,7 +9,6 @@ import (
 )
 
 const CONCAT rune = '~'
-const UNION int = 0
 
 func isOperator(c rune) bool {
 	if c == '*' || c == '|' || c == CONCAT {
@@ -126,15 +125,19 @@ func thompson(re string) *State {
 			}
 			s1.output = s2.output
 			nfa = append(nfa, s1)
-		case '*':
+		case '*': // Create a 0-state, concat the popped state after it, concat the 0-state after the popped state
 			s1 := pop(&nfa)
+			stateToAdd := &State{}
+			stateToAdd.transitions = make(map[int][]*State)
+			stateToAdd.content = EPSILON
+			stateToAdd.isEmpty = true
+			stateToAdd.isKleene = true
+			stateToAdd.output = append(stateToAdd.output, stateToAdd)
 			for i := range s1.output {
-				s1.output[i].transitions[s1.content] = append(s1.output[i].transitions[s1.content], s1)
+				s1.output[i].transitions[stateToAdd.content] = append(s1.output[i].transitions[stateToAdd.content], stateToAdd)
 			}
-			// Reset output to s1 (in case s1 was a union operator state, which has multiple outputs)
-			s1.output = nil
-			s1.output = append(s1.output, s1)
-			nfa = append(nfa, s1)
+			stateToAdd.transitions[s1.content] = append(stateToAdd.transitions[s1.content], s1)
+			nfa = append(nfa, stateToAdd)
 		case '|':
 			s1 := pop(&nfa)
 			s2 := pop(&nfa)
@@ -143,7 +146,7 @@ func thompson(re string) *State {
 			s3.output = append(s3.output, s1, s2)
 			s3.transitions[s1.content] = append(s3.transitions[s1.content], s1)
 			s3.transitions[s2.content] = append(s3.transitions[s2.content], s2)
-			s3.content = UNION
+			s3.content = EPSILON
 			s3.isEmpty = true
 
 			nfa = append(nfa, &s3)